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The first truly Earth-like alien planet is likely to be spotted next year, an epic discovery that would cause humanity to reassess its place in the universe.

While astronomers have found a number of exoplanets over the last few years that share one or two key traits with our own world ? such as size or inferred surface temperature ? they have yet to bag a bona fide "alien Earth." But that should change in 2013, scientists say.

"I'm very positive that the first Earth twin will be discovered next year," said Abel Mendez, who runs the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo.

Astronomers discovered the first exoplanet orbiting a sunlike star in 1995. Since they, they've spotted more than 800 worlds beyond our own solar system, and many more candidates await confirmation by follow-up observations.

NASA's prolific Kepler Space Telescope, for example, has flagged more than 2,300 potential planets since its March 2009 launch. Only 100 or so have been confirmed to date, but mission scientists estimate that at least 80 percent will end up being the real deal.

Kepler telescope needs to witness three of these"transits" to detect a planet, so its early discoveries were tilted toward close-orbiting worlds (which transit more frequently). But over time, the telescope has been spotting more and more distantly orbiting planets ? including some in the habitable zone.

An instrument called HARPS (short for High Accuracy Radial velocity Planet Searcher) is also a top contender, having already spotted a number of potentially habitable worlds. HARPS, which sits on the European Southern Observatory's 3.6-meter telescope in Chile, allows researchers to detect the tiny gravitational wobbles that orbiting planets induce in their parent stars.

Whenever the first Earth twin is confirmed, the discovery will likely have a profound effect on humanity.

"We humans will look up into the night sky, much as we gaze across a large ocean," Marcy told SPACE.com via email. "We will know that the cosmic ocean contains islands and continents by the billions, able to support both primitive life and entire civilizations."